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According to the CDC, vaccine shedding is the release or discharge of any of the vaccine components in or outside of the body. This most likely occurs when a vaccine contains a live weakened version of the virus.

From a previous lesson, we learned the following vaccines contain live viruses: Measles, Mumps, and Rubella (MMR), Rotavirus, Smallpox, Chickenpox (Varicella), Yellow Fever, and Influenza. This is why the CDC advises against vaccination for patients that could shed onto immunocompromised family members (see below).

Live Influenza vaccine (OPV):

Measles, Mumps, and Rubella (MMR) vaccine:

Chickenpox (Varicella) vaccine:

Additionally, the Rotavirus manufacturer insert states the following:

The manufacturer also lists shedding as a potential adverse reaction:

How long does a vaccine shed?

On the Smallpox manufacturer insert, the following is disclosed about shedding:

For MMR, the following study identified a potential shedding period for recently vaccinated patients:

Also, a measles vaccine-type virus has been found in the throat of a child after vaccination:

This is why it is important for officials to test if recent outbreaks are caused by wild or vaccine strains.

What about polio?

Thankfully the oral polio vaccine that contained a live virus is no longer used in the United States. Per the CDC, the polio vaccine caused “vaccine-associated paralytic poliomyelitis (VAPP)”. Here is more information about the polio vaccine strain:

However, the CDC also states the following about the inactivated polio vaccine:

Because of this, there is a possibility of a shedding-type event of other vaccines. There simply isn’t enough data to determine that other types of vaccines do or do not perform a shedding-like event after vaccination.